A method for production of nanoMOF and prelimiary

ORIGINAL PAPER
NUKLEONIKA 2012;57(4):581−583
A method for production of nanoMOF
and prelimiary characterization
by selected analytical techniques
Wojciech Starosta,
Bożena Sartowska,
Krzysztof Łyczko,
Jan Maurin,
Andrzej Pawlukojć,
Lech Waliś,
Marek Buczkowski
Abstract. Metal-organic frameworks (MOFs) are a class of porous hybrid materials comprising metal ion-based vertices and multitopic organic ligands (linkers). The possibility of combining a wide range of metals with similarly large
number of available ligands opens ways to design the structures meeting specific purposes. At present, many potential
applications of MOFs may require them to be constructed at the nanometer length scale (nanoMOFs). The possibility
of filling the track-etched membrane pores with MOF HKUST-1 has been demonstrated in this work.
Key words: HKUST-1 • metal-organic frameworks (MOFs) • solvothermal method • template synthesis
Introduction
W. Starosta, B. Sartowska, K. Łyczko, A. Pawlukojć,
L. Waliś, M. Buczkowski
Institute of Nuclear Chemistry and Technology,
16 Dorodna Str., 03-195 Warsaw, Poland,
Tel.: +48 22 504 1230, Fax: +48 22 811 1532,
E-mail: [email protected]
J. Maurin
National Nuclear Research Centre (NCBJ),
7 Andrzeja Sołtana Str., 05-400 Otwock, Poland
Received: 29 November 2011
Accepted: 10 January 2012
Metal-organic frameworks (MOFs) are a class of porous
hybrid materials comprising metal ion-based vertices
and multitopic organic ligands (linkers) which serve to
connect the vertices into three-dimensional periodic
structures. The possibility of combining a wide range of
metals with similarly large number of available ligands
opens ways to design the structures meeting specific
purposes. In particular, the shape and dimensions of
pores, preferred adsorption sites for gas molecules and
binding energy for adsorbed molecules are the primary
factors when considering specific application.
From the beginning, interest for these materials has
been driven by a possible use for greenhouse gases removal by physisorption, hydrogen storage for future clean
energy technologies and for highly selective separation
of gaseous mixtures [3–7]. At present, many potential applications of MOFs may require them to be constructed
at the nanometer length scale (nanoMOFs) [2] because
nanoscopic dimensions are essential to:
– provide MOFs with higher surface areas than do
their macroscopic counterparts, opening up novel
avenues for tuning their catalytic, ion exchange,
separation, sensing and sorption properties;
– provide MOFs that can be integrated on surfaces
or directly incorporated into the polymer matrix,
to create thin MOF membranes;
– provide materials of sufficiently small and uniform
sizes, dispersible and bio-compatible for their use
as delivery vehicles (e.g. drugs, vaccines, etc.) and
diagnostic agents for biomedical applications.
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W. Starosta et al.
The well known copper(II) benzene-1,3,5-tricarboxylate
MOF (HKUST-1) has been selected for deposition
inside the pores of track-etched membranes. It forms
a face centred cubic crystalline framework that is com-
posed of dimeric cupric tetracarboxylate units shown in
Fig. 1. They give an intersecting 3D-channel system with
a micropore diameter of 0.7–0.8 nm shown in Fig. 2. Synthesis of HKUST-1 has been performed by a solvothermal method. Benzene-1,3,5-tricarboxylic acid (1.9664 g,
0.009 mol) was dissolved in ethanol (20 ml) with stirring.
Cupric nitrate trihydrate (4.48 g, 0.018 mol) was dissolved
in distilled water (10 ml) in another flask. The two solutions were then mixed and stirred at room temperature
for 16 h. The resulting viscous mixture was transferred
into a Teflon lined stainless steel autoclave. The autoclave
was heated inside a hot air oven at 413 K for 48 h. The reaction vessel was then left to cool to room temperature.
Small octahedral in shape, blue coloured single
crystal has been selected from reaction product for
structure determination by single crystal X-ray diffraction with an Xcalibur-R single crystal diffractometer.
The measurements confirmed the presence of face
centred cubic structure of Cu3(BTC)2(H2O)3, (BTC –
benzene-1,3,5-tricarboxylate), with lattice parameter
of 26.346 Å.
Reaction product after drying has been analysed by
scanning electron microscopy and infrared spectroscopy. The scanning electron microscopy photograph
shown in Fig. 3 reveals a mixture of crystalline material
having broad range of dimensions.
Infrared absorption spectra of the 1,3,5-tribenzenocarboxylic acid and its copper(II) complex shown
in Fig. 4 were recorded at room temperature in the
range 400–4000 cm–1 using KBr pellets with a Bruker
Equinox 55 FTIR spectrometer. All functional groups of
1,3,5-tribenzenocarboxylic acid (hydroxyl and carbonyl)
form bonds with copper(II) ions in the obtained complex. This is confirmed by the lack of very broad band
in the range 3200–2500 originating from the stretching
vibrations of the OH groups in uncoordinated ligand.
In addition, the partial loss of the C=O double bond
character after complexation of this carboxylic acid to
the copper(II) ions is shown by the shift of the ν(C=O)
bands to lower wavelengths, from 1723 cm–1 in free
Fig. 2. [Cu3(BTC)2(H2O)3]n polymer framework viewed down
the [100] direction, showing nanochannels with fourfold symmetry.
Fig. 3. SEM photograph for HKUST-1 showing crystallites
with different dimensions.
Fig. 1. Dicopper(II) tetracarboxylate building block for
HKUST-1.
Promising properties of MOF’s coupled with the
ease by which their structures can be modified makes
MOFs one of the most exciting, diverse, and rapidly
growing areas of modern materials chemistry research.
Our group activities in this field are concerned mainly
with nanoscale MOFs synthesis by a template synthesis
method. Development of hybrid track-etched membrane having the pores filled with MOF material is also
of primary interest. Such composite membranes can find
application in sensing and removal of harmful gases,
particularly gaseous radioactive species released during nuclear fuel reprocessing or in the case of nuclear
accidents.
Experimental
A method for production of nanoMOF and prelimiary characterization by selected analytical techniques
Fig. 4. Infrared spectra of HKUST-1 complex (red) and BTC
ligand (black).
583
method developed in [1] based on crystallization of
the Cu BTC complex from dimethylsulphoxide (DMSO)
solution of metal salt and BTC ligand. In our case,
1.170 g of cupric nitrate trihydrate and 0.580 g of BTC
ligand have been dissolved in 5 g of DMSO. Droplets of
this solution were deposited on the surface of plasma activated PET track-etched membrane with a pore diameter of
1 μm. For plasma activation home made dielectric barrier
discharge device working in the air was utilized. Thanks
to the plasma chemical modification in the discharge,
excellent wettability of membrane surface was achieved
resulting in spilling of droplets and thin layer coverage
of the membrane. The samples were allowed to stay at
ambient temperature for few days. SEM photograph
shown in Fig. 5 revealed the presence of octahedral in
shape, nanoscale crystals with dimensions significantly
below 1 μm filling the fraction of the pores.
Conclusions
The possibility of filling the track-etched membrane
pores with MOF HKUST-1 has been demonstrated.
Research on finding the optimal conditions for this
process and subsequently to grow thin MOF layer over
the membrane surface are in progress.
References
Fig. 5. SEM photograph of the PET membrane surface with
octahedral in shape, nanoscale crystals.
ligand to 1625 cm–1 in complex. Moreover the broad
band around 3420 cm–1 for copper(II) complex gives
evidence for the presence of water molecules in this
compound. It is in agreement with single crystal X-ray
diffraction measurements for studied complex. Crystal
structure investigations show that all copper(II) ions are
coordinated additionally by one water molecule.
For deposition of nanoMOF on sensitive material like PET polymer foil, much smaller temperature
conditions would be preferable. We adopted the
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